In the field of servers or the like, for the era of big data, there are increased needs for accessing large volume data such as a database (DB) at high speed. The trend to increase the capacity of the main storage unit including a DRAM (Dynamic Random Access Memory) has not been able to follow the above-described needs, due to the deficiency of three-dimensional memory packaging technology (TSV). There is a difference of approximately 106 between throughputs (latency) of a DRAM and a SAS (Serial Attached SCSI) connection SSD (Solid State Drive) or an HDD (Hard Disk Drive), as an auxiliary storage unit.
PCI (Peripheral Component Interconnect Express) connection SSD (PCI-SSD), which has high-speed response between the DRAM and the SAS connection SSD (SAS-SSD), has been commercialized. This market is expected to grow bigger.
As a result of prior art search after the present invention, PTL 1 and PTL 2 have been extracted as related matters. PTL 1 discloses an FBDIMM (Fully Buffered DIMM), in which a flash memory and a DRAM are mounted in different DIMMs (Dual Inline Memory Module) and connected in a daisy chain manner with a serial transmission system, through the buffer element for serial transmission mounted in each module. The memory controller transmits a serialized control signal, an address signal, and a write data signal to the DIMM, and receives a serialized read data signal, in accordance with an FBDIMM signal transmission protocol.
PTL 2 discloses a memory module, in which an SDRAM chip (DRAM) of 256 Mb, a NAND type flash memory chip (FLASH) of 264 Mb, and a control circuit chip controlling the DRAM and the FLASH are mounted in one package (BGA package). The memory module secures a region for copying a part of or entire data of the FLASH, and transfers the data from the FLASH to the DRAM in advance, thereby enabling to read the data of the FLASH approximately at the same speed as that of the DRAM.